The ultimate objective of our work is to gain sufficient insight into the mechanism of fragmentation of organic compounds in the mass spectrometer so that the principal features of the mass spectrum of a compound of known constitution can be predicted. With this information, it should then be possible to utilize the mass spectrum of an unknown compound for purposes of structure elucidation. In view of the extreme sensitivity of the method and the very small quantities required for mass spectral measurements, this technique has proved and will continue to prove itself enormously useful in the field of natural products. Our own emphasis is now concentrating almost exclusively upon sterols since recent work in the marine chemical field has shown the occurrence of dozens of novel sterols which have no terrestrial counterpart. Consequently model sterols are being synthesized that contain many of the unusual features typical of these novel sterols so that their mass spectral fragmentation can be predicted. Once known, this information will be extraordinarily useful in analyzing rapidly by gas chromatography/mass spectrometry techniques large numbers of marine extracts and focus on those fractions where mass spectrometry indicates the presence of potentially new structures. This information is also needed for further work on compouter aided prediction of mass spectral data. Direct application of these techniques to the structure elucidation of novel marine sterols will be carried out.